China’s navy has issued multiple warnings to a US surveillance aircraft to leave the airspace over artificial islands Beijing is building to strengthen its claims over disputed territory in the South China Sea.

The messages, witnessed by a US TV crew aboard the P8-A Poseidon surveillance aircraft, came soon after the Pentagon said it was considering military patrols in the region and amid concerns that Chinese activity was raising the risk of a confrontation between Washington and Beijing.

CNN reported that a Chinese naval vessel issued eight warnings to the US plane on Wednesday, in an apparent effort to establish a no-fly zone near the artificial islands. When US pilots pointed out that they were flying through international airspace, an exasperated Chinese radio operator responded: “This is the Chinese navy … you go!”

China urges caution from US over South China Sea disputes

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The exchange is an indication of what could lie ahead if the US decides to send military aircraft and ships to the area, where China is locked in a battle of wills over ownership of reefs with the Philippines and several other countries.

The incident occurred in the skies above Fiery Cross reef, where China has triggered international anger with the construction of an early-warning radar station and other military facilities on reclaimed land.

TV footage taken from the aircraft showed construction and dredging activity on the newly built islands, together with a strong Chinese naval presence. Experts believe the islands, which include a 3,000-metre-long runway, could be fully operational by the end of the year.

Capt Mike Parker, commander of US surveillance aircraft deployed in Asia, said he believed the aircraft had been challenged by a nearby Chinese vessel.

High stakes surveillance over the South China Sea. Video: CNN

“We were just challenged 30 minutes ago and the challenge came from the Chinese navy,” he told CNN. “I’m highly confident it came from ashore, this facility here,” he added, pointing to an early-warning radar station on Fiery Cross Reef.

Ambitious Chinese reclamation work has added to tensions around the Spratly archipelago, where the Philippines, Vietnam, Malaysia, Brunei and Taiwan have competing territorial claims. The area includes vital commercial shipping lanes responsible for annual trade of about $5tn (£3.2bn).

China claims 90% of the South China Sea, which is believed to be rich in oil and gas deposits. Earlier this week, the US deputy secretary of state, Antony Blinken, warned that Chinese land reclamation work was damaging stability in the region and could even lead to conflict.

“As China seeks to make sovereign land out of sandcastles and redraw maritime boundaries, it is eroding regional trust and undermining investor confidence,” he said. “Its behaviour threatens to set a new precedent whereby larger countries are free to intimidate smaller ones, and that provokes tensions, instability and can even lead to conflict.”

In response, the Pentagon is considering sending military aircraft and ships to the area to ensure freedom of navigation around China’s growing number of artificial islands. “We are considering how to demonstrate freedom of navigation in an area that is critical to world trade,” a US official said, speaking on condition of anonymity. “The US and its allies have a very different view than China over the rules of the road in the South China Sea.”

Beijing says it will not stop reclamation work, with China’s foreign minister, Wang Yi, describing its sovereignty claims as “hard as a rock”.